JP2011193124A - Reference signal transmission scheduling device, base station device and reference signal transmission scheduling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To create a reference signal transmission schedule suitable for estimating the maximum Doppler frequency of a terminal. <P>SOLUTION: The transmission schedule is provided with: a maximum Doppler frequency estimation period for the terminal to transmit a reference signal to a base station in order to estimate the maximum Doppler frequency; and a channel quality measurement period for the terminal to transmit the reference signal to the base station in order to measure quality of a communication channel in the direction going from the terminal to the base station, and an SRS scheduler 10 creates the reference signal transmission schedule suitable for estimating the maximum Doppler frequency to the maximum Doppler frequency estimation period, and creates the reference signal transmission schedule to the channel quality measurement period based on the maximum Doppler frequency estimated using the reference signal received at the base station in the maximum Doppler frequency estimation period. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a reference signal transmission scheduling apparatus, a base station apparatus, and a reference signal transmission scheduling method.

  In recent years, standardization work for LTE (Long Term Evolution) systems has been promoted in the 3GPP (3rd Generation Partnership Project) of the standardization organization. The LTE system is a cellular system that aims to realize high-speed communication with a communication speed of 100 Mbps or higher in the downlink (direction from the base station to the terminal) and a communication speed of 50 Mbps or more in the uplink (direction from the terminal to the base station). This is a wireless communication system. The LTE system supports frequency division duplex and time division duplex.

  In the frequency division duplex scheme, the base station instructs the terminal about the period at which the terminal transmits a downlink channel quality indicator (CQI) to the base station in order to know the downlink reception quality. The terminal periodically feeds back the downlink CQI to the base station according to the instruction. On the other hand, in order to know the uplink reception quality, the base station uses an SRS-related parameter that defines a cycle in which the terminal transmits a reference signal (referred to as a sounding reference signal (SRS)) to the base station. Notify the terminal. Then, the terminal periodically transmits the SRS to the base station according to the SRS related parameters, and the base station receives the SRS and measures the uplink channel quality.

3GPP TS 36.211 V8.7.0, May 2009 3GPP TS 36.213 V8.7.0, May 2009 3GPP TS36.331 V8.6.0, June 2009

  Since the downlink CQI and the uplink channel quality measurement SRS transmitted by the terminal are transmitted from the terminal to the base station using the uplink radio resource, in order to effectively use the radio resource, It is desirable to set a period for feeding back downlink CQI and SRS-related parameters according to the channel quality fluctuation period of the terminal.

  The channel quality variation period of the terminal can be expressed using a coherence time. Here, the coherence time is a time during which fluctuations in the channel quality of the terminal can be ignored. In general, the coherence time representing the channel quality fluctuation period of the terminal is directly proportional to the reciprocal of the maximum Doppler frequency of the terminal. That is, the higher the maximum Doppler frequency, the shorter the coherence time, and the lower the maximum Doppler frequency, the longer the coherence time.

  Accordingly, if the maximum Doppler frequency of the terminal can be accurately estimated, the channel quality fluctuation period of the terminal can be obtained with high precision. Therefore, the downlink CQI feedback period or the SRS-related frequency is determined according to the channel quality fluctuation period of the terminal. By setting parameters, it becomes possible to use radio resources efficiently.

  The present invention has been made in view of such circumstances, and a reference signal transmission scheduling apparatus, a base station apparatus, and a reference that can create a reference signal transmission schedule suitable for estimating the maximum Doppler frequency of a terminal. It is an object of the present invention to provide a signal transmission scheduling method.

  In order to solve the above problems, a reference signal transmission scheduling apparatus according to the present invention is a reference signal transmission scheduling apparatus for creating a transmission schedule of a reference signal to be transmitted from a terminal to a base station in a wireless communication system. A maximum Doppler frequency estimation period in which the terminal transmits the reference signal to the base station to estimate the frequency, and the terminal transmits the reference signal to the base station to measure the quality of the communication channel in the direction from the terminal to the base station. A channel quality measurement period for transmission is provided in the transmission schedule, a reference signal transmission schedule suitable for estimating the maximum Doppler frequency is created for the maximum Doppler frequency estimation period, and the channel quality measurement period is Using the reference signal received at the base station during the maximum Doppler frequency estimation period. Based on the estimated maximum Doppler frequency it has been, characterized by creating a reference signal transmission schedule.

  In the reference signal transmission scheduling apparatus according to the present invention, the first maximum Doppler frequency estimated using the reference signal received by the base station during the maximum Doppler frequency estimation period, and the base station during the channel quality measurement period. Switching from the channel quality measurement period to the maximum Doppler frequency estimation period based on a difference from the second maximum Doppler frequency estimated using the received reference signal.

  In the reference signal transmission scheduling apparatus according to the present invention, when the difference continuously falls outside the allowable range a predetermined number of times, the channel quality measurement period is switched to the maximum Doppler frequency estimation period.

  In the reference signal transmission scheduling apparatus according to the present invention, a terminal that transmits the reference signal in the maximum Doppler frequency estimation period, a terminal that transmits the reference signal in the channel quality measurement period, and the difference in the channel quality measurement period The terminal management part which manages the terminal used as the object which determines this is provided.

  In the reference signal transmission scheduling apparatus according to the present invention, a first registration table for registering a terminal that transmits the reference signal in the maximum Doppler frequency estimation period, and a terminal that transmits the reference signal in the channel quality measurement period are registered. And a third registration table for registering a terminal for which the difference is determined during the channel quality measurement period.

  A base station apparatus according to the present invention uses any of the reference signal transmission scheduling apparatuses described above and a reference signal received from a terminal during a maximum Doppler frequency estimation period in a reference signal transmission schedule created by the reference signal transmission scheduling apparatus. A maximum Doppler frequency estimation unit for estimating a maximum Doppler frequency, and a channel quality measurement for measuring a communication channel quality using a reference signal received from a terminal during a channel quality measurement period in a reference signal transmission schedule created by the reference signal transmission scheduling apparatus And a section.

  A reference signal transmission scheduling method according to the present invention is a reference signal transmission scheduling method for creating a transmission schedule of a reference signal to be transmitted from a terminal to a base station in a wireless communication system, and the terminal uses the base station to estimate a maximum Doppler frequency. A maximum Doppler frequency estimation period for transmitting the reference signal to a channel quality measurement period for the terminal to transmit the reference signal to the base station in order to measure the quality of the communication channel in the direction from the terminal to the base station. Creating a reference signal transmission schedule suitable for estimating the maximum Doppler frequency with respect to the maximum Doppler frequency estimation period provided in the transmission schedule; and the maximum Doppler frequency estimation period with respect to the channel quality measurement period The maximum frequency estimated using the reference signal received by the base station. Based on the plug frequency, characterized in that it comprises the steps of creating a reference signal transmission schedule, the.

  According to the present invention, it is possible to create a reference signal transmission schedule suitable for estimating the maximum Doppler frequency of a terminal.

1 is a schematic configuration diagram of an LTE system according to an embodiment of the present invention. It is a flowchart which shows the procedure of the SRS transmission scheduling method which concerns on the same embodiment. It is a flowchart which shows the procedure of the SRS transmission scheduling method which concerns on the same embodiment. It is a flowchart which shows the procedure of the SRS transmission scheduling method which concerns on the same embodiment. It is a flowchart which shows the procedure of the SRS transmission scheduling method which concerns on the same embodiment. It is an example of a structure of the phase 1 registration table 34 shown in FIG. It is a structural example of the phase 2 registration table 36 shown in FIG. It is an example of a structure of the follow-up determination phase registration table 38 shown in FIG. It is an example of a structure of the follow-up determination phase registration table 38 shown in FIG. It is an example of a structure of the phase 1 registration table 34 shown in FIG. It is an example of the maximum Doppler frequency estimation period and channel quality measurement period which concern on one Embodiment of this invention. It is an example of a general SRS transmission schedule. An excerpt from the LTE standard. It is an example of the selection procedure of the SRS multiplexing method which concerns on one Embodiment of this invention. It is another example of the selection procedure of the SRS multiplexing method which concerns on one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an LTE system according to an embodiment of the present invention. FIG. 1 shows a configuration related to uplink SRS transmission and a configuration related to uplink channel quality measurement.

  In FIG. 1, the base station 2 includes an SRS scheduler 10, an information input unit 12, a channel quality measurement unit 14, a maximum Doppler frequency estimation unit 16, an SRS reception unit 18, and an SRS related parameter notification unit 20. The terminal 100 has an SRS transmission unit 102. The base station 2 notifies the terminal 100 of SRS related parameters. Terminal 100 transmits SRS to base station 2 in accordance with the SRS-related parameters. The SRS related parameter is information for specifying an uplink SRS transmission schedule.

Here, the SRS related parameters will be briefly described. There are the following parameters as SRS-related parameters.
(1) srs-Bandwidth: SRS transmission band for each terminal, which is represented by the number of resource blocks (RB). The RB is a radio resource allocation unit having a certain frequency bandwidth (the number of subcarriers) and a certain time width (the number of OFDM symbols).
(2) srs-HoppingBandwidth: a hopping pattern in SRS transmission. For example, when the system band of the LTE system is “RB number = 50”, the SRS band is “RB number = 48”, and the terminal's SRS transmission band (srs-Bandwidth) is “RB number = 4”, “srs When -HoppingBandwidth = 3 ", SRS hopping on the frequency axis is not performed, and when" srs-HoppingBandwidth ≠ 3 ", SRS hopping on the frequency axis is performed.
(3) duration: indicates either “single” for SRS transmission only once or “indefinite” for continuous SRS transmission.
(4) srs-ConfigIndex: Indicates the SRS transmission cycle and the offset value of the transmission subframe (Subframe). The SRS transmission period supported by the LTE system is “2 milliseconds (mS), 5 mS, 10 mS, 20 mS, 40 mS, 80 mS, 160 mS, 320 mS”, and the offset value of the transmission subframe is 0 to “determined SRS transmission period −1 ”.
(5) transmissionComb: indicates selection of a subcarrier in which SRS is arranged. In the case of “transmissionComb = 0”, the SRS is arranged on the odd subcarrier. In the case of “transmissionComb = 1”, SRSs are arranged in even-numbered subcarriers.
(6) cyclicShift: indicates a code selected when code-multiplexing SRSs of different terminals. Code multiplexing by cyclic shift can be performed for SRSs of different terminals having the same srs-Bandwidth.
(7) freqDomainPosition: SRS transmission band logical position (nRRC) for each terminal. nRRC is a logical identifier (logical ID) of a frequency band composed of four RBs. In addition, the physical position of the SRS transmission band includes the srs-BandwidthConfig that is a parameter of the SRS transmittable band that is common to the sectors, the srs-Bandwidth, srs-HoppingBandwidth, and the freqDomainPosition (nRRC) that are parameters for each terminal, and the number of SRS transmissions. And determined from

  Returning to FIG. In the base station 2 shown in FIG. 1, the SRS scheduler 10 determines SRS related parameters. The information input unit 12 inputs information used by the SRS scheduler 10 to the SRS scheduler 10. The channel quality measurement unit 14 measures the uplink channel quality using the uplink SRS (reception SRS) received by the SRS reception unit 18. The maximum Doppler frequency estimation unit 16 estimates the maximum Doppler frequency using the received SRS. The SRS receiving unit 18 receives an uplink SRS transmitted by the terminal 100. The SRS related parameter notification unit 20 notifies the terminal 100 of the SRS related parameters determined by the SRS scheduler 10.

  In terminal 100 shown in FIG. 1, SRS transmission section 102 transmits an uplink SRS to the base station according to the SRS-related parameters notified from base station 2.

  The SRS scheduler 10 illustrated in FIG. 1 includes a terminal (UE) management unit 30, a scheduling unit 32, a phase 1 registration table 34, a phase 2 registration table 36, and a follow-up determination phase registration table 38.

  In this embodiment, a maximum Doppler frequency estimation period (phase 1) and a channel quality measurement period (phase 2) are provided in the uplink SRS transmission schedule. The maximum Doppler frequency estimation period is a period in which the terminal 100 transmits an SRS to the base station 2 in order to estimate the maximum Doppler frequency. The SRS scheduler 10 creates an SRS transmission schedule suitable for estimating the maximum Doppler frequency for the maximum Doppler frequency estimation period.

  The channel quality measurement period is a period during which terminal 100 transmits SRS to base station 2 in order to measure uplink channel quality. The SRS scheduler 10 creates an SRS transmission schedule based on the maximum Doppler frequency estimated using the received SRS received by the base station 2 in the maximum Doppler frequency estimation period with respect to the channel quality measurement period. Thereby, the SRS transmission schedule according to the channel quality fluctuation period of the terminal can be created for the channel quality measurement period.

  The UE management unit 30 manages the terminal 100 that transmits the SRS during the maximum Doppler frequency estimation period and the terminal 100 that transmits the SRS during the channel quality measurement period. In addition, the UE management unit 30 manages the terminal 100 that is a determination target in the maximum Doppler frequency tracking determination phase.

  The scheduling unit 32 determines an SRS related parameter in the maximum Doppler frequency estimation period and an SRS related parameter in the channel quality measurement period.

  The phase 1 registration table 34 is a table for registering the terminal 100 that transmits the SRS during the maximum Doppler frequency estimation period. The phase 2 registration table 36 is a table for registering the terminal 100 that transmits the SRS during the channel quality measurement period. The tracking determination phase registration table 38 is a table for registering the terminal 100 to be determined in the tracking determination phase of the maximum Doppler frequency.

  Next, the operation of the base station 2 according to the present embodiment will be described with reference to the flowcharts of FIGS. 2 to 5 are flowcharts showing a procedure of the SRS transmission scheduling method according to the present embodiment.

  In the uplink of the LTE system, SRS is transmitted in each subframe. In the following explanation, subframe numbers (consecutive integers, which increase by 1 with the passage of time) along the temporal order of the subframes are provided, and the subframe numbers are used to follow the passage of time. Next, the operation of the base station 2 will be described. FIG. 11 shows the passage of time using the subframe numbers used in the following description.

  Further, in the following description, a subframe that is a current SRS transmission scheduling target is referred to as a current target subframe.

  First, the process of FIG. 2 will be described. The process of FIG. 2 is started when the current target subframe becomes the (n-1) th subframe. In step S1, the UE management unit 30 detects the terminal 100 that has newly entered the RRC_connected state from the RRC_Idle state. As a result, if the terminal 100 is detected, the process proceeds to step S3. If the terminal 100 is not detected, the process of FIG. In step S <b> 3, the UE management unit 30 registers the detected terminal 100 in the “subframe number = n” field of the phase 1 registration table 34.

  FIG. 6 shows a configuration example of the phase 1 registration table 34. In the example of FIG. 6, the terminal 100 (terminal identifier (terminal ID): UE_A) newly in the RRC_connected state is detected, and the terminal 100 (terminal ID: UE_A) is “subframe number = n ”is registered.

  Note that the RRC_connected state is a state in which the base station 2 and the terminal 100 can transmit and receive RRC messages. The SRS related parameter is notified from the base station 2 to the terminal 100 by an RRC message.

  Next, the process of FIG. 3 will be described. The process of FIG. 3 is started when the current target subframe becomes the nth subframe. In step S <b> 11, the UE management unit 30 notifies the scheduling unit 32 of the terminal ID of the terminal 100 registered in the “subframe number = n” field of the phase 1 registration table 34. Then, the scheduling unit 32 determines whether or not the SRS related parameter of the maximum Doppler frequency estimation period starting from the nth subframe can be assigned to the terminal 100 of the notified terminal ID. When the scheduling unit 32 can allocate the SRS-related parameter of the maximum Doppler frequency estimation period starting from the n-th subframe to the terminal 100, the scheduling unit 32 allocates the SRS-related parameter of the maximum Doppler frequency estimation period. The scheduling unit 32 notifies the SRS related parameter notification unit 20 of the assignment result of the SRS related parameters for the terminal 100. The SRS related parameter notification unit 20 notifies the terminal 100 of the allocation result of the SRS related parameters.

  In FIG. 11, the maximum Doppler frequency estimation period starting from the nth subframe is composed of P subframes from the nth subframe to the (n + P-1) th subframe. The length of the maximum Doppler frequency estimation period (number of subframes: P) is set in advance and input from the information input unit 12.

  As a result of step S11, if an SRS related parameter can be assigned, the process proceeds to step S13 (step S12, YES), and if an SRS related parameter cannot be assigned, the process proceeds to step S14 (step S12, NO).

  In step S <b> 13, the UE management unit 30 registers the terminal 100 determined to be able to assign the SRS related parameter in step S <b> 11 in the “subframe number = n + P” column of the phase 2 registration table 36.

  FIG. 7 shows a configuration example of the phase 2 registration table 36. In the example of FIG. 7, the maximum Doppler frequency starting from the nth subframe for the terminal 100 (terminal ID: UE_A) registered in the “subframe number = n” column of the phase 1 registration table 34 of FIG. 6. It is determined that the SRS-related parameters for the estimation period can be assigned, and the terminal 100 (terminal ID: UE_A) is registered in the “subframe number = n + P” column of the phase 2 registration table 36.

  In step S <b> 14, the UE management unit 30 registers the terminal 100 determined to be unable to allocate the SRS related parameter in step S <b> 11 in the “subframe number = n + 1” column of the phase 1 registration table 34. For the terminal 100, when the current target subframe becomes the (n + 1) th subframe, the process of FIG. 3 is executed again.

  Next, the process of FIG. 4 will be described. The process of FIG. 4 is started when the current target subframe becomes the (n + P) th subframe. In step S <b> 21, the UE management unit 30 notifies the maximum Doppler frequency estimation unit 16 of the terminal ID of the terminal 100 registered in the “subframe number = n + P” column of the phase 2 registration table 36. Then, the maximum Doppler frequency estimation unit 16 receives from the terminal 100 during the maximum Doppler frequency estimation period from the nth subframe to the (n + P−1) th subframe with respect to the terminal 100 of the notified terminal ID. The maximum Doppler frequency is estimated using the received SRS. The maximum Doppler frequency estimation unit 16 notifies the UE management unit 30 of the estimated value of the maximum Doppler frequency together with the terminal ID. The UE management unit 30 records the notified estimated value of the maximum Doppler frequency together with the terminal ID as an estimated reference value.

  In FIG. 11, the estimated value (estimation reference value) of the maximum Doppler frequency is obtained using the received SRS received from the terminal 100 during the maximum Doppler frequency estimation period from the nth subframe to the (n + P-1) th subframe. It has been calculated.

  Next, in step S22, the UE management unit 30 notifies the scheduling unit 32 of the terminal ID of the terminal 100 registered in the “subframe number = n + P” column of the phase 2 registration table 36 together with the estimated reference value. Then, the scheduling unit 32 assigns, to the terminal 100 with the notified terminal ID, SRS related parameters in the channel quality measurement period starting from the (n + P) th subframe based on the estimated reference value of the terminal 100. It is determined whether or not When the scheduling unit 32 can assign the SRS related parameter of the channel quality measurement period starting from the (n + P) th subframe to the terminal 100, the scheduling unit 32, based on the estimation reference value of the terminal 100, Assign SRS related parameters for channel quality measurement period. The scheduling unit 32 notifies the SRS related parameter notification unit 20 of the assignment result of the SRS related parameters for the terminal 100. The SRS related parameter notification unit 20 notifies the terminal 100 of the allocation result of the SRS related parameters.

In FIG. 11, the channel quality measurement period starting from the (n + P) th subframe is composed of Q subframes from the (n + P) th subframe to the (n + P + Q-1) th subframe. The length of the channel quality measurement period (number of subframes: Q) is set in advance and input from the information input unit 12. The length Q (unit: mS) of the channel quality measurement period can be determined by the following equation, for example.
Q = T2_SRS × ceil (P ÷ T1_SRS)
Where T1_SRS is the SRS transmission period (unit is mS) in the maximum Doppler frequency estimation period, T2_SRS is the SRS transmission period (unit is mS) in the channel quality measurement period, and P is the length of the maximum Doppler frequency estimation period (unit is mS). It is. ceil (X) is the smallest integer greater than or equal to the value of X.

  As a result of step S22, when the SRS related parameter can be assigned, the process proceeds to step S24 (step S23, YES), and when the SRS related parameter cannot be assigned, the process proceeds to step S25 (step S23, NO).

  In step S24, the UE management unit 30 registers the terminal 100 determined to be able to assign the SRS-related parameter in step S22 in the “subframe number = n + P + Q” field of the tracking determination phase registration table 38.

  FIG. 8 shows a configuration example of the follow-up determination phase registration table 38. In the example of FIG. 8, the channel starting from the (n + P) -th subframe with respect to the terminal 100 (terminal ID: UE_A) registered in the “subframe number = n + P” column of the phase 2 registration table 36 of FIG. It is determined that the SRS-related parameters of the quality measurement period can be assigned, and the terminal 100 (terminal ID: UE_A) is registered in the “subframe number = n + P + Q” column of the tracking determination phase registration table 38.

  In step S25, the UE management unit 30 registers the terminal 100 determined to be unable to assign the SRS related parameter in step S22 in the “subframe number = n + P + 1” field of the phase 2 registration table 36. For this terminal 100, when the current target subframe becomes the (n + P + 1) th subframe, the processing of FIG. 4 is performed again (however, since the estimated reference value has been calculated, the estimated reference value in step S21). Is excluded).

  Next, the process of FIG. 5 will be described. The processing in FIG. 5 is started when the current target subframe becomes the (n + P + Q) th subframe. In step S <b> 31, the UE management unit 30 notifies the maximum Doppler frequency estimation unit 16 of the terminal ID of the terminal 100 registered in the “subframe number = n + P + Q” column of the follow-up determination phase registration table 38. The maximum Doppler frequency estimation unit 16 then transmits the terminal 100 of the notified terminal ID from the terminal 100 during the channel quality measurement period from the (n + P) th subframe to the (n + P + Q-1) th subframe. The maximum Doppler frequency is estimated using the received SRS received. The maximum Doppler frequency estimation unit 16 notifies the UE management unit 30 of the estimated value of the maximum Doppler frequency together with the terminal ID. The UE management unit 30 records the notified estimated value of the maximum Doppler frequency together with the terminal ID as an estimated follow-up value.

  Next, in step S32, the UE management unit 30 calculates the difference between the estimated reference value and the estimated follow-up value for the terminal 100 registered in the “subframe number = n + P + Q” column of the follow-up determination phase registration table 38. To do. Next, in step S33, the UE management unit 30 determines whether the difference is within a predetermined allowable range. As a result, when the difference is within the allowable range, the process proceeds to step S34 (step S33, YES), and when the difference is outside the allowable range, the process proceeds to step S35 (step S33, NO).

  In step S34, the UE management unit 30 sets the terminal 100 whose difference between the estimated reference value and the estimated follow-up value is within an allowable range in the “subframe number = current target subframe number + Q” field of the follow-up determination phase registration table 38. Register with.

  FIG. 9 shows a configuration example of the follow-up determination phase registration table 38. In the example of FIG. 9, the estimated reference value and the estimated follow-up value for the terminal 100 (terminal ID: UE_A) registered in the “subframe number = n + P + Q” column of the follow-up determination phase registration table 38 in FIG. As a result of the determination of the difference, the terminal 100 (terminal ID: UE_A) is passed and registered in the column of “subframe number = current target subframe number (n + P + Q) + Q” in the tracking determination phase registration table 38.

  In FIG. 11, the estimated value (estimated follow-up value) of the maximum Doppler frequency is obtained using the received SRS received from the terminal 100 during the channel quality measurement period from the (n + P) th subframe to the (n + P + Q-1) th subframe. As a result of being calculated and the difference between the estimated reference value and the estimated follow-up value being determined, the result is acceptable. Thereby, the next channel quality measurement period from the (n + P + Q) th subframe to the (n + P + Q + Q-1) th subframe becomes valid for the terminal 100.

  In step S35, the UE management unit 30 continuously counts the difference between the estimated reference value and the estimated follow-up value for the terminal 100 whose difference between the estimated reference value and the estimated follow-up value is outside the allowable range. Increases by 1. Note that the initial value of the continuous number is zero.

  Next, in step S36, the UE management unit 30 determines whether the continuous count is within a predetermined allowable range. As a result, when the continuous number is within the allowable range, the process proceeds to step S34 (step S36, YES), and when the continuous number is outside the allowable range, the process proceeds to step S37 (step S36, NO).

  In step S <b> 37, the UE management unit 30 determines that the terminal 100 whose number of consecutive times that the difference between the estimation reference value and the estimated follow-up value has failed is outside the allowable range, “subframe number = current target” in the phase 1 registration table 34. Register in the column of “subframe number + 1”.

  FIG. 10 shows a configuration example of the phase 1 registration table 34. In the example of FIG. 10, the allowable range of the number of consecutive times in which the difference between the estimated reference value and the estimated follow-up value has been rejected is up to once, and the failure is continuously outside the allowable range twice or more. In FIG. 10, when the terminal 100 (terminal ID: UE_A) registered in the “subframe number = n + P + Q + Q” column of the follow-up determination phase registration table 38 of FIG. 9 is estimated for the (n + P + Q + Q) -th subframe. Although the difference between the reference value and the estimated follow-up value is acceptable, the estimated reference value and the estimated follow-up are obtained when the current target subframe is the (n + P + 3 × Q) th subframe and the (n + P + 4 × Q) th subframe. The difference from the value was continuously rejected. Thereby, since the number of consecutive times “2 times” in which the difference between the estimated reference value and the estimated follow-up value has failed is out of the allowable range, the terminal 100 (terminal ID: UE_A) becomes “ Subframe number = current target subframe number (n + P + 4 × Q) +1 ”. As a result, the terminal 100 (terminal ID: UE_A) is switched from the channel quality measurement period to the maximum Doppler frequency estimation period.

  In the example of FIG. 11, the allowable range of the number of consecutive times in which the difference between the estimated reference value and the estimated follow-up value has been rejected is up to once, and the fail is continuously outside the allowable range twice or more. In FIG. 11, the difference between the estimated reference value and the estimated follow-up value was acceptable when the current target subframe is the (n + P + Q) th subframe and the (n + P + 2 × Q) th subframe, When the subframe was the (n + P + 3 × Q) th subframe and when the subframe was the (n + P + 4 × Q) th subframe, the failure was continuously rejected. As a result, since the consecutive number of times “2 times” in which the difference between the estimation reference value and the estimated follow-up value has failed is outside the allowable range, the channel 100 is measured from the channel quality measurement period to the maximum Doppler frequency estimation period. Switch to. In this case, when the current target subframe becomes the (n + P + 4 × Q + 1) -th subframe, the processing of FIG. 3 is started, and the maximum Doppler frequency starting from the (n + P + 4 × Q + 1) -th subframe for the terminal 100 It is determined whether the SRS-related parameters for the estimation period can be assigned.

  Next, a method for assigning SRS-related parameters will be described.

  FIG. 12 shows an example of a general SRS transmission schedule. In the example of FIG. 12, srs-BandwidthConfig has 48 RBs. The srs-Bandwidth of the terminal 100 (terminal ID: UE_A) is 24 RBs, the srs-Bandwidth of the terminal 100 (terminal ID: UE_B) is 12, and the srs-Bandwidth of the terminal 100 (terminal ID: UE_C). Has 4 RBs. Moreover, the same transmissionComb, cyclicShift, and srs-ConfigIndex are applied to each terminal 100 (terminal IDs: UE_A, UE_B, UE_C). The nRRC of the terminal 100 (terminal ID: UE_A) is 0, the nRRC of the terminal 100 (terminal ID: UE_B) is 6, and the nRRC of the terminal 100 (terminal ID: UE_C) is 9. Moreover, srs-HoppingBandwidth is 0. Thereby, the physical position of the SRS band of each terminal 100 (terminal ID: UE_A, UE_B, UE_C) for each SRS transmission as shown in FIG. 12 is realized.

  In the present embodiment, the scheduling unit 32 performs the maximum Doppler frequency estimation period and the channel quality measurement period so that the assignment of the SRS related parameter in the maximum Doppler frequency estimation period and the assignment of the SRS related parameter in the channel quality measurement period do not collide. A subcarrier in which the SRS is arranged is distinguished. For example, it is possible to selectively use odd-numbered subcarriers and even-numbered subcarriers. In this case, for example, the SRS in the maximum Doppler frequency estimation period is arranged in odd subcarriers, and the SRS in the channel quality measurement period is arranged in even subcarriers. Or the reverse may be sufficient. Thereby, the assignment of the SRS-related parameters in the maximum Doppler frequency estimation period and the assignment of the SRS-related parameters in the channel quality measurement period can be performed completely independently. Therefore, the assignment of the SRS-related parameters in the maximum Doppler frequency estimation period and the assignment of the SRS-related parameters in the channel quality measurement period may be performed in parallel or sequentially.

[SRS-related parameter allocation method for maximum Doppler frequency estimation period]
A method for assigning SRS-related parameters in the maximum Doppler frequency estimation period will be described.
(1) In general, in the method of estimating the maximum Doppler frequency of the terminal, using the fact that the time correlation ρ (τ) of the impulse response of the Rayleigh wave can be expressed using the first type 0th order Bessel function, Estimate the maximum Doppler frequency of the terminal. In a wireless communication system, in order to obtain an impulse response of a Rayleigh wave, it is desirable to arrange a signal for estimating the maximum Doppler frequency over as wide a band as possible. Therefore, the maximum Doppler frequency can be accurately estimated by arranging the signal for estimating the maximum Doppler frequency over the widest possible band. Therefore, in order to accurately estimate the maximum Doppler frequency, an SRS transmission band (srs-Bandwidth) as wide as possible is allocated to the SRS scheduling target terminal in the maximum Doppler frequency estimation period.

  Specifically, the transmittable bandwidth of the SRS scheduling target terminal is obtained based on the maximum transmission power and desired reception quality of the SRS scheduling target terminal. At this time, when the transmittable bandwidth of the SRS scheduling target terminal cannot be obtained, a predetermined default value of the transmittable bandwidth is used. Then, the maximum SRS band that is equal to or less than the transmittable band of the SRS scheduling target terminal is set as the srs-Bandwidth of the SRS scheduling target terminal from among the SRS bands that can be taken in the SRS band supported by the LTE system.

FIG. 13 shows the LTE standard extracted from Non-Patent Document 1. In the LTE standard shown in FIG. 13, when the system band of the LTE system is “number of RBs = 50”, the SRS bands “m _{SRS, 0} , m _{SRS, 1} , m _{SRS, 2} for each terminal supported by the LTE system” , M _{SRS, 3} ”and item number“ B _SRS ”. For example, in the base station 2 in which the SRS band of the LTE system is “C _SRS = 0”, when the transmittable band of the SRS scheduling target terminal is “number of RBs = 20”, “m _{SRS, 0} , m _{SRS, 1} , M _{SRS, 2} , m _{SRS, 3} ”and“ B _SRS ”with 20 or less RBs are“ B _SRS = 2 ”and“ B _SRS = 3 ”, and the minimum value“ B _SRS ” The SRS bandwidth “m _{SRS, 2} : RB number = 12” for each terminal corresponding to “ _SRS = 2” is set in the srs-Bandwidth of the SRS scheduling target terminal.

(2) When there are a plurality of SRS scheduling target terminals in the maximum Doppler frequency estimation period in the current target subframe, priority is given to a terminal having a large amount of transmission data, and SRS related parameters in the maximum Doppler frequency estimation period are assigned.

(3) In order to accurately estimate the maximum Doppler frequency, SRS hopping in the frequency axis is not performed. Accordingly, “srs-HoppingBandwidth = 3” is set.

(4) SRS is continuously transmitted. Therefore, the duration is set to “indefinite”.

(5) In the present embodiment, the SRS of the maximum Doppler frequency estimation period is arranged on odd subcarriers. Therefore, “transmissionComb = 0” is set.

(6) A method for determining cyclicShift, freqDomainPosition, and srs-ConfigIndex will be described.
There are three types of SRS multiplexing methods between different terminals: frequency multiplexing using freqDomainPosition, time multiplexing using transmission subframe offset value of srs-ConfigIndex, and code multiplexing using cyclicShift. The order of the SRS multiplexing method is determined according to the LTE system policy. 14 and 15 show the selection procedure of the SRS multiplexing method.

  FIG. 14 is a flowchart illustrating a procedure for selecting an SRS multiplexing method when maximizing the number of accommodated terminals is a policy of the LTE system. In FIG. 14, SRS-related parameter allocation to the SRS scheduling target terminal is attempted in the order of code multiplexing, frequency multiplexing, and time multiplexing. In FIG. 14, it is first determined in step S101 whether code multiplexing is possible. If code multiplexing is possible, cyclic shift, freqDomainPosition, and srs-ConfigIndex when code multiplexing is performed are determined in step S102. On the other hand, if code multiplexing is not possible, it is determined in step S103 whether frequency multiplexing is possible. If frequency multiplexing is possible, cyclic shift, freqDomainPosition and srs-ConfigIndex for frequency multiplexing are determined in step S104. On the other hand, if frequency multiplexing is not possible, it is determined in step S105 whether there is a transmission subframe offset value to which a band that can be represented by srs-BandwidthConfig can be allocated. If there is a transmission subframe offset value, time multiplexing is performed in step S106. When performing, determine cyclicShift, freqDomainPosition, and srs-ConfigIndex.

  FIG. 15 is a flowchart illustrating a selection procedure of an SRS multiplexing method when minimization of SRS mutual interference between different terminals is a policy of the LTE system. In FIG. 15, SRS-related parameter allocation to the SRS scheduling target terminal is attempted in the order of frequency multiplexing, time multiplexing, and code multiplexing. In FIG. 15, it is first determined in step S201 whether frequency multiplexing is possible. If frequency multiplexing is possible, cyclic shift, freqDomainPosition, and srs-ConfigIndex when frequency multiplexing is performed are determined in step S202. On the other hand, if frequency multiplexing is not possible, it is determined in step S203 whether there is a transmission subframe offset value to which a band that can be represented by srs-BandwidthConfig can be allocated. If there is a transmission subframe offset value, time multiplexing is performed in step S204. When performing, determine cyclicShift, freqDomainPosition, and srs-ConfigIndex. On the other hand, if time multiplexing is also impossible, it is determined in step S205 whether code multiplexing is possible. If code multiplexing is possible, cyclic shift, freqDomainPosition, and srs-ConfigIndex when code multiplexing is performed are determined in step S206.

Next, cyclicShift, freqDomainPosition, and srs-ConfigIndex when performing frequency multiplexing will be described.
The terminal 100 to which the SRS-related parameter for the maximum Doppler frequency estimation period has been assigned is set as a frequency multiplexing candidate terminal. If there is an nRRC that satisfies the following conditional expression using the transmission subframe offset value and cyclicShift of the frequency multiplexing candidate terminal in the nRRC that is an empty band other than the nRRC of the frequency multiplexing candidate terminal, the frequency multiplexing Determine that you can.
nRRC mod (srs-Bandwidth ÷ 4) = 0
However, the minimum unit of srs-Bandwidth is 4 RBs. A mod (B) is the remainder when A is divided by B.

  When frequency multiplexing is performed, the minimum value of nRRC that satisfies the above conditional expression is set in the freqDomainPosition of the SRS scheduling target terminal. Then, the transmission subframe offset value of the terminal 100 that is the frequency multiplexing partner and the SRS transmission period in the maximum Doppler frequency estimation period are set in the srs-ConfigIndex of the SRS scheduling target terminal, and the Cyclic Shift is selected from among the assignable Cyclic Shifts. The Cyclic Shift with the smallest identifier is set to the Cyclic Shift of the SRS scheduling target terminal. The SRS transmission period in the maximum Doppler frequency estimation period is set in advance and input from the information input unit 12.

Next, cyclicShift, freqDomainPosition, and srs-ConfigIndex when performing time multiplexing will be described.
If an SRS transmission band represented by srs-BandwidthConfig can be allocated in a subframe to be time multiplexed, it is determined that time multiplexing can be performed. In the case of time multiplexing, “nRRC = 0” is set in the freqDomainPosition of the SRS scheduling target terminal. Then, the transmission subframe offset value of the terminal 100 that is the time multiplexing partner and the SRS transmission period in the maximum Doppler frequency estimation period are set in the srs-ConfigIndex of the SRS scheduling target terminal, and the Cyclic Shift is selected from among the assignable Cyclic Shifts. The Cyclic Shift with the smallest identifier is set to the Cyclic Shift of the SRS scheduling target terminal. The SRS transmission period in the maximum Doppler frequency estimation period is set in advance and input from the information input unit 12.

Next, cyclicShift, freqDomainPosition, and srs-ConfigIndex when performing code multiplexing will be described.
It is determined that an SRS scheduling target terminal having the same srs-Bandwidth as the terminal 100 to which the SRS-related parameter of the maximum Doppler frequency estimation period has been assigned can be code-multiplexed. In the case of code multiplexing, the freqDomainPosition and srs-ConfigIndex of the terminal 100 that is the code multiplexing partner are similarly set in the SRS scheduling target terminal. Then, a cyclic shift different from the cyclic shift of the terminal 100 to be code-multiplexed among the assignable cyclic shifts is set as the cyclic shift of the SRS scheduling target terminal.

[Allocation method of SRS-related parameters in channel quality measurement period]
A method for assigning SRS-related parameters in the channel quality measurement period will be described.

(1) The transmittable bandwidth of the SRS scheduling target terminal is obtained based on the maximum transmission power and the desired reception quality of the SRS scheduling target terminal. At this time, when the transmittable bandwidth of the SRS scheduling target terminal cannot be obtained, a predetermined default value of the transmittable bandwidth is used. Further, the required SRS transmission band of the SRS scheduling target terminal is obtained based on the estimation reference value of the SRS scheduling target terminal and the SRS transmission period in the channel quality measurement period. The SRS transmission period in the channel quality measurement period is set in advance and input from the information input unit 12. Note that the coherence time representing the channel quality fluctuation period of the terminal is directly proportional to the reciprocal of the maximum Doppler frequency of the terminal.

  When the transmittable band of the SRS scheduling target terminal is larger than the required SRS transmission band of the SRS scheduling target terminal, the minimum that is greater than the required SRS transmission band and less than the transmittable band from the selectable SRS transmission bands Is set to the srs-Bandwidth of the SRS scheduling target terminal.

  On the other hand, when the transmittable band of the SRS scheduling target terminal is less than or equal to the required SRS transmission band of the SRS scheduling target terminal, the maximum SRS transmission band that is equal to or less than the transmittable band is selected from the selectable SRS transmission bands. Set to srs-Bandwidth of the scheduling target terminal.

A specific example of srs-Bandwidth in the LTE standard shown in FIG. 13 will be described. For example, in the base station 2 in which the system band of the LTE system is “RB number = 50” and the SRS band of the LTE system is “C _SRS = 0”, the transmittable band of the SRS scheduling target terminal is “number of RBs”. = 30 ”and the required SRS transmittable bandwidth is“ Number of RBs = 10 ”, the number of RBs among“ m _{SRS, 0} , m _{SRS, 1} , m _{SRS, 2} , m _{SRS, 3} ”is 10 or more and 30 The following “B _SRS ” is “B _SRS = 1” and “B _SRS = 2”, and the SRS bandwidth “m _{SRS, 2} ” for each terminal corresponding to the maximum value “B _SRS = 2” of the item numbers. : RB count = 12 ”is set to the srs-Bandwidth of the SRS scheduling target terminal.

(2) In the current target subframe, when there are a plurality of SRS scheduling target terminals in the channel quality measurement period, priority is given to a terminal having a large transmission data amount, and an SRS related parameter in the channel quality measurement period is assigned.

(3) In order to obtain a gain of frequency diversity (Diversity), hopping of SRS in the frequency axis is performed over the SRS band of the LTE system. Accordingly, “srs-HoppingBandwidth = 0” is set.

(4) SRS is continuously transmitted. Therefore, the duration is set to “indefinite”.

(5) In the present embodiment, the SRS in the channel quality measurement period is arranged on even subcarriers. Accordingly, “transmissionComb = 1” is set. In this embodiment, the SRS in the maximum Doppler frequency estimation period is arranged in odd subcarriers.

(6) cyclicShift, freqDomainPosition, and srs-ConfigIndex are set in the same manner as in the above-described maximum Doppler frequency estimation period. However, the partner terminal 100 to be multiplexed is the terminal 100 to which the SRS related parameters in the channel quality measurement period have been assigned.

  According to the embodiment described above, a maximum Doppler frequency estimation period and a channel quality measurement period are provided in the SRS transmission schedule, and an SRS transmission schedule suitable for estimating the maximum Doppler frequency with respect to the maximum Doppler frequency estimation period is created. For the channel quality measurement period, an SRS transmission schedule is created based on the maximum Doppler frequency estimated using the SRS received by the base station during the maximum Doppler frequency estimation period. According to this SRS transmission schedule, the maximum Doppler frequency can be accurately estimated by the maximum Doppler frequency estimation period. Since the coherence time representing the channel quality fluctuation period of the terminal is directly proportional to the reciprocal of the maximum Doppler frequency of the terminal, the channel quality measurement period is determined based on the highly accurate maximum Doppler frequency estimate (estimation reference value). The SRS transmission schedule along the channel quality fluctuation period of the terminal can be created. As a result, uplink radio resources can be used efficiently.

  Further, when the difference between the maximum Doppler frequency (estimated tracking value) estimated using the SRS received by the base station during the channel quality measurement period and the estimated reference value is outside the allowable range, the maximum Doppler from the channel quality measurement period. By switching to the frequency estimation period, it is possible to update the estimation reference value according to the actual situation. This makes it possible to maintain a certain quality with respect to the SRS transmission schedule in the channel quality measurement period.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

DESCRIPTION OF SYMBOLS 2 ... Base station, 10 ... SRS scheduler, 12 ... Information input part, 14 ... Channel quality measurement part, 16 ... Maximum Doppler frequency estimation part, 18 ... SRS receiving part, 20 ... SRS related parameter notification part, 30 ... Terminal (UE ) Management unit 32... Scheduling unit 34... Phase 1 registration table 36... Phase 2 registration table 38.

Claims (7)

In a wireless communication system, a reference signal transmission scheduling apparatus for creating a transmission schedule of a reference signal that a terminal transmits to a base station,
The maximum Doppler frequency estimation period in which the terminal transmits the reference signal to the base station to estimate the maximum Doppler frequency, and the terminal to the base station to measure the quality of the communication channel in the direction from the terminal to the base station. A channel quality measurement period for transmitting a signal, provided in the transmission schedule,
Creating a reference signal transmission schedule suitable for estimating the maximum Doppler frequency for the maximum Doppler frequency estimation period;
For the channel quality measurement period, create a reference signal transmission schedule based on the maximum Doppler frequency estimated using the reference signal received by the base station in the maximum Doppler frequency estimation period;
A reference signal transmission scheduling apparatus.   The first maximum Doppler frequency estimated using the reference signal received by the base station during the maximum Doppler frequency estimation period, and the first maximum Doppler frequency estimated using the reference signal received by the base station during the channel quality measurement period. 2. The reference signal transmission scheduling apparatus according to claim 1, wherein the reference signal transmission scheduling apparatus switches from the channel quality measurement period to the maximum Doppler frequency estimation period based on a difference between the maximum Doppler frequency and the maximum Doppler frequency.   3. The reference signal transmission scheduling apparatus according to claim 2, wherein when the difference is outside the allowable range for a predetermined number of times, the channel quality measurement period is switched to the maximum Doppler frequency estimation period.   Managing a terminal that transmits the reference signal in the maximum Doppler frequency estimation period, a terminal that transmits the reference signal in the channel quality measurement period, and a terminal that is a target for determining the difference in the channel quality measurement period The reference signal transmission scheduling apparatus according to claim 2, further comprising a terminal management unit. A first registration table for registering a terminal that transmits the reference signal in the maximum Doppler frequency estimation period;
A second registration table for registering a terminal that transmits the reference signal in the channel quality measurement period;
A third registration table for registering a terminal for which the difference is determined in the channel quality measurement period;
The reference signal transmission scheduling apparatus according to claim 4, further comprising: The reference signal transmission scheduling apparatus according to any one of claims 1 to 5,
A maximum Doppler frequency estimation unit that estimates a maximum Doppler frequency using a reference signal received from a terminal in a maximum Doppler frequency estimation period in a reference signal transmission schedule created by the reference signal transmission scheduling device;
A channel quality measurement unit for measuring communication channel quality using a reference signal received from a terminal during a channel quality measurement period in a reference signal transmission schedule created by the reference signal transmission scheduling device;
A base station apparatus comprising: A reference signal transmission scheduling method for creating a transmission schedule of a reference signal that a terminal transmits to a base station in a wireless communication system,
The maximum Doppler frequency estimation period in which the terminal transmits the reference signal to the base station to estimate the maximum Doppler frequency, and the terminal to the base station to measure the quality of the communication channel in the direction from the terminal to the base station. A channel quality measurement period for transmitting a signal, provided in the transmission schedule,
Creating a reference signal transmission schedule suitable for estimating a maximum Doppler frequency for the maximum Doppler frequency estimation period;
Creating a reference signal transmission schedule based on the maximum Doppler frequency estimated using the reference signal received at the base station during the maximum Doppler frequency estimation period for the channel quality measurement period;
A reference signal transmission scheduling method comprising:

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